This invention relates to ultrasonic imaging and especially to a system having a horn transducer or simulated horn transmitter and to a method of imaging.
Conventional ultrasonic B-scan imaging systems use a single-element, fixed aperture transducer to form the beam. Because of this, these systems remain in focus over a limited depth of field. As an approach to focusing over a large depth of field, a number of authors have proposed using a conical transducer (see FIG. 1). However, for the physical dimensions that are consistent with contact B-scan imaging, the cone angle must be small (FIG. 2) to ensure that focusing is maintained to large depths. As a result, the focusing properties in the near field do not represent a significant improvement over a conventional B-scan transducer.
Variable focus annular arrays have also been proposed to increase the depth of field. These systems and those with conical transducers can be extremely complex and hence costly to manufacture.